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Insights into base-free OsO4-catalyzed aminohydroxylations employing chiral ligands.

ABSTRACT: Attempts to perform the OsO4-catalyzed enantioselective base-free aminohydroxylation of ?,?-disubstituted enoates are described. Low yields and racemic products were obtained in the presence of standard chiral ligands, suggesting the occurrence of a "Second Cycle" process due to slow hydrolysis of the amino alcohol product from the Os metal center. Support for this hypothesis was provided by the slightly improved enantioselectivity (60:40 er) obtained with an amino alcohol ligand. Based on density functional theory calculations, it is proposed that the lack of significant enantioselectivity is due to a low-energy (3 + 2) oxo/imido cycloaddition transition state without the chiral ligand in the Second Cycle that outcompetes protonolysis in the First Cycle.

SUBMITTER: Cardon JM

PROVIDER: S-EPMC6374041 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Insights into base-free OsO<sub>4</sub>-catalyzed aminohydroxylations employing chiral ligands.

Cardon Joseph M JM Coombs James C JC Ess Daniel H DH Castle Steven L SL

Tetrahedron 20190111 8

Attempts to perform the OsO<sub>4</sub>-catalyzed enantioselective base-free aminohydroxylation of β,β-disubstituted enoates are described. Low yields and racemic products were obtained in the presence of standard chiral ligands, suggesting the occurrence of a "Second Cycle" process due to slow hydrolysis of the amino alcohol product from the Os metal center. Support for this hypothesis was provided by the slightly improved enantioselectivity (60:40 er) obtained with an amino alcohol ligand. Bas ...[more]

PMID: 30774161

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